The driver, an Italian national originally from Senegal, reportedly claimed he set the bus on fire in protest over migrant deaths at sea.
A Milan court sentenced Ousseynou Sy after he was found guilty of forced confinement with terrorist intent and prosecutors had demanded the 24 year sentence, media said.
Sy had driven his school bus with 51 pupils onboard towards Milan airport in March last year as he was transporting the 12-13 year olds to school in Crema, east of Milan.
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Police blocked the bus and the children managed to escape through a back window that had been smashed by security forces.
Sy said at the time he had heard the voices of drowned migrant children urging him to take action, according to media reports.
Two of the children on the bus, who had Egyptian and Moroccan nationality, were given Italian citizenship in 2019 in recognition of their bravery in helping others escape during the hijacking.